Polytetrafluoroethylene fabrics are woven from strands of polytetrafluoroethylene. Polytetrafluoroethylene is commonly known as Teflon and is a registered trademark of E. I. DuPont de Nemours & Company, Inc.
Polytetrafluoroethylene fabrics, fibers, yarns, or threads are available in many varieties from a variety of distributors. Typical of the polytetrafluoroethylene is a fabric sold by Stern and Stern Textiles, Incorporated, New York, N.Y., called T41-30. It is a leno weave cloth with 45.times.21 ends/inch and has a thickness of 0.010 inch. It has a weight of 4.35 ounces per square yard.
Polytetrafluoroethylene fabrics, fibers, yarns, or threads are used for a variety of purposes including such things as filters, screens, reinforcement, packing, insulation, liners and gasket materials. They are also used as supports for fluoropolymer ion exchange active films. Such films are commonly used as ion exchange membranes in electrolytic cells.
When used as filters, it is important for the polytetrafluoroethylene filters to be water wettable. Otherwise, they will not operate efficiently because of the large pressure drop when aqueous materials are being filtered. However, it is not easy to make polytetrafluoroethylene water wettable. The present invention, makes a water wettable polytetrafluoroethylene.
Polytetrafluoroethylene fabrics are limp and exhibit low friction, thread to thread. This causes fabrics made from such materials to become distorted under normal handling and causes holes to appear without breaking threads.
The prior art has attempted to coat polytetrafluoroethylene fabrics, fibers, yarns, or threads by using mechanical lamination equipment. Other prior art has attempted to attach polytetrafluoroethylene fabrics, fibers, yarns, or threads to ion exchange membrane films using heat treatment and extraction procedures rather than stabilizing the cloth itself (see U.S. Pat. No. 4,272,560).
Other known relevant art includes: U.S. Pat. Nos. 3,770,567; 3,925,135; 4,272,560; 4,324,606; 4,399,183; 4,341,605; and 4,437,951.
Burrell [J. Paint Tech., Volume 41, page 495 (1969)]predicts a non-crystalline polymer will dissolve in a solvent of similar solubility parameter without chemical similarity, association, or any intermolecular force. However, he fails to mention anything about the solubility of polymers demonstrating crystallinity.
It would be highly desirable to be able to coat polytetrafluoroethylene fabrics, fibers, yarns, or threads such that when they are woven into fabrics, the fabrics will be sized. The present invention provides such a method.